Cytokines, such as IL-8, associated with acute respiratory distress syndrome (32), and IL-6, associated with severe cytokine-release syndrome, can occur in chronic lymphocytic leukemia patients after treatment with rituximab, an anti-CD20 monoclonal antibody (33).The underlying disease (polycythemia vera) in the second case-patient is associated with Janus kinase 2 mutation V617F, which leads to constitutive tyrosine phosphorylation activity that promotes cytokine hypersensitivity, including IL-3 and stem cell factor (34,35). The gene discussed is JAK2; the disease is acquired polycythemia vera.